The preforms are introduced into the plant one after another in a vertical position, neck uppermost, pushed to cause them to enter a gripping and loading member of the plant, such as a notched horizontal wheel. For correct feed, it is necessary not only for the preforms to be pushed positively into the gripper member, but also for them to arrive at this member without any discontinuity, all arranged in the required vertical position, and without the preforms being nested inside one another.
Commonly, in order for all these conditions to be met simultaneously, the preforms, contained in a loading hopper, are taken therefrom via elevator, and are then conveyed to the start of the plant under gravity using a chute conveyor in the form of guides; at the top of this chute conveyor there is an orientation device comprising an input hopper into which the preforms are tipped in bulk from the elevator, together with the actual orientation mechanism proper (commonly consisting of orienting rollers) and various elements intended for introducing the preforms into the chute conveyor one by one and for eliminating any preforms nested inside one another, etc.
In very high capacity plants capable of producing several thousand, if not several tens of thousand containers per hour, the device for orienting the preforms is not only positioned at a very great height but is also very large in size, and its opening may be situated at a height of several meters. It is therefore necessary for it to be associated with appropriate equipment (walkway with guard rails, ladder, etc.) so that the supervisory and maintenance personnel can have perfectly safe access to the orientation device and to the devices associated therewith (the elevator connecting the loading hopper to the input hopper, etc.) which are located at a height. This equipment, generally made of metal, is very expensive and very bulky. Furthermore, the preform feed device arranged in this way occupies a great deal of space.
What is more, the chute conveyor essentially consists of two parallel guides on which the preforms rest via their flange. Owing to the inclination of the guides and because of the approximately horizontal position of the flanges due to the fact that the preforms are situated generally vertically the flanges rest on the guides at just two symmetrically opposed points on their periphery, and therefore in a way that is not very stable; what this means is that the movement of the preforms under gravity along the guides is uneven because of non-constant friction and is accompanied by a swinging of the preforms, this being something that may have consequences detrimental to correct and uniform operation of the plant (as it may cause preforms to jam, to be ejected, etc.).
The users of such plants therefore have a pressing need for feed devices which are less expensive and less bulky while at the same time are capable of moving the preforms along more uniformally and without the possibility of incidents.
It is precisely an object of the invention to meet these requirements and to propose means which are better able than the current devices to meet the various requirements of current practice.